In the pending application Ser. No. 100220, filed Sept. 23, 1987, an azeotrope-like composition comprising 1,1,2-trichloro-1,2,2-trifluoroethane, methanol and 1,2-dichloroethylene was disclosed as an effective cleaning solvent composition, particularly in cleaning modern electronic circuit boards.
As indicated in the above-cited application, the current industrial processes for soldering electronic components to circuit boards involve coating the entire circuit side of the board with a flux composition and, thereafter, passing this coated side of the board over preheaters, and then through molten solder. The flux composition cleans the conductive metal parts and promotes adhesion of the solder. Commonly used fluxes consist, for the most part of rosin used alone or with activating additives such as amine hydrochlorides or oxalic acid derivatives.
After soldering, which thermally degrades part of the rosin, flux and flux residues are often removed from the board with an organic solvent composition.
Since requirements for the removal of contaminants from circuit boards are very stringent, most current industrial circuit board cleaning processes involve the use of vapor defluxing techniques. In a conventional operation of a vapor defluxer, the board is passed through a sump of boiling organic solvent which removes the bulk of the rosin (including thermally degraded rosin), and thereafter through a sump containing freshly distilled solvent, and finally through solvent vapor over a boiling sump which provides a final rinse with a clean solvent which condenses on the circuit board. In addition, the board can also be sprayed with distilled solvent before the final rinse.
While the azeotrope or azeotrope-like composition of 1,1,2-trichloro-1,2,2-trifluoroethane, methanol, and 1,2-dichloroethylene is an excellent solvent system for cleaning circuit boards, for practical industrial use, this solvent system, as is the case with any solvent system, should be stabilized against compositional changes during both use and long term storage. Changes, such as oxidation, polymerization, interaction of components and the like, may generate products which adversely affect the circuit boards being cleaned or the solvent composition itself.
It is therefore an object of the present invention to provide an azeotrope or an azeotrope-like composition of 1,1,2-trichloro-1,2,2-trifluoroethane, methanol and 1,2-dichloroethylene which is stable during use and long term storage and which minimizes the formation of undesirable reaction products which may adversely affect the cleaning of electronic circuit boards.